1. Field of the Invention
The invention relates to a combustion chamber structure of a spark-ignition internal combustion engine.
2. Description of Related Art
A spark-ignition internal combustion engine in which tumble flow is produced in a combustion chamber and is guided to the vicinity of an ignition plug is known in the art. For example, in a combustion chamber structure of this type of internal combustion engine as described in Japanese Patent Application Publication No. 2013-113126 (JP 2013-113126 A), an ignition plug region provided around an ignition plug hole, and four port regions provided around two intake ports and two exhaust ports are delimited or separated from each other by means of ridges, and each of the ignition plug region and the four ports regions is formed in a substantially semi-spherical shape that is concaved upward in the combustion chamber. With the combustion chamber structure, the tumble flow that collapses at around the compression top dead center can be concentrated in the vicinity of the ignition plug. Accordingly, the ignition performance can be improved, and the combustion efficiency can be enhanced.